Facebook (FB -3.6%) has fallen below $27 in the wake of Bernstein's critical report and news of a new Google local ad sales push. Other volatile Internet and social media names are unsurprisingly also diving: ZNGA -4.2%. GRPN -7.9%. YELP -6.8%. RENN -5.1%. Z -5.9%. Henry Blodget, who previously set a $16-$24 PT range for Facebook, discusses how multiple compression appears inevitable for the company as growth slows, judging by the histories of tech giants.